Wall-stabilized high-pressure mercury and metal iodide vapour discharge lamp with outer envelope

ABSTRACT

A wall-stabilised high-pressure mercury vapour discharge lamp having an ignition voltage of less than 500 volts. The discharge vessel of the lamp contains in addition to mercury the iodides of one or more other metals and a mixture of neon and argon. The discharge vessels is surrounded by an outer envelope which is filled with a mixture of nitrogen and neon. Furthermore a selective hydrogen getter is present within the outer envelope.

United States Patent 1 91 Beijer et a1.

WALL-STABILIZED HIGH-PRESSURE MERCURY AND METAL IODIDE VAPOUR DISCHARGE LAMP WITH OUTER ENVELOPE Inventors: Louis Benjamin Beijer; Antonius Jozephus Gerardus Cornelis Drieseen; Cornelis Adrlanus Joannes Jacobs, all of Emmasingel, Eindhoven, Netherlands Assignee: U.S. Philips Corporation, New York,

Filed: July 8, 1971 Appl. No.: 160,656

Foreign Application Priority Data July 31, 1970 Netherlands 7011321 Int. Cl H0lj 61/26, HOlj 61/34 111 3,753,018 143.1 Aug. 14, 1973 [58] Field of Search 313/184, 25, 26,

[56] References Cited UNITED STATES PATENTS 3,626,229 12/1971 Spacil et al. 313/184 X' 2,176,134 10/1939 Holst 313/25 Primary Examiner-Palmer C. Demeo Attorney-Frank R. Trifari 4 Claims, 1 Drawing Figure PATENIED All: 14 I978 IN VEN TOR S AG EN WALL-STABILIZED HIGH-PRESSURE MERCURY AND METAL IODIDE VAPOUR DISCHARGE LAMP WITH OUT-ER ENVELOPE The invention relates to wall-stabilised high-pressure mercury vapour discharge lamps having an ignition voltage of less than 500 volts and consisting of a quartz glass discharge vessel and an outer envelope encompassing this vessel, the dischargevessel containing in addition to mercury a mixture of neon and argon as well as iodide of at least one of the elements sodium, lithium, cadmium, thallium, indium, tin, dysprosium, gallium, lead and scandium.

'For some years the conventional wall-stabilized highpressure mercury vapour discharge lamps have been considerably improved as regards their output and light composition by introducing iodides of other metals into the discharge space and by constructing and operating the lamp in such a manner that intensive lines of the metals of the added iodides occur in the spectrum of the emitted light. In case of suitable choice of the iodides, for example, lamps may be manufactured in this manner which emit substantially white light and make a very satisfactory colour rendition possible. At the same time the output has been brought to the very high values of from 90 to H lumens/Watt due to these steps. For obtaining these results sodium, lithium, cadmium, thallium, indium, tin, dysprosium and scandium is preferably used and in many cases more than one of these elements is present as an iodide in the discharge vessel. lf instead of or in addition to these elements lead and/or gallium is introduced into the discharge vessel an increase of the ultraviolet radiation is obtained.

ln the above-described known lamps an ignition gas is used in the discharge vessel, so as to decrease the ignition voltage. The object is to bring the ignition voltage at any rate below 500 volts, because 500 volts is the lower limit of the so-called EHT range in many countries. When using voltages of more than 500 volts, all kinds of safety precautions are to be taken which render an installation of course more expensive. Originally only argon was used for this purpose as an ignition gas at a pressure of, for example, to 40 Torr at C. However, it was found that when using argon as an ignition gas only the ignition voltage may lie far below the above-mentioned limit of SOO voIts at the beginning of the lifetime of the lamps, but this ignition voltage could surpass this limit after several hundred operating hours. Of course this is not only a drawback in view of the above-mentioned safety precautions, but it is furthermore very much detrimental because the ignition equipment for obtaining the. required ignition voltage must be proportioned for the highest voltage. As a result the ignition apparatus becomes of course more complicated and more expensive. This increase of the ignition voltage occurs to a much lesser extent in lamps without additions.

Following the known fact that in high-pressure mercury vapour discharge lamps without an addition of other elements and iodine the original ignition voltage could be decreased by using a mixture of argon and neon instead of argon only (in which the quantity of neon is much larger than the quantity of argon), experiments were performed with lamps containing these additions and likewise employing a mixture of neon and argon as an ignition gas. As regards the expected decrease of the original ignition voltage, the result was substantially nil. However, a reduction in the increase of the ignition voltage during the lifetime occurred particularly in lamps for wattages of more than 300 W.

A known drawback of the use of neon in the quartz glass discharge vessel is that it must be surrounded by an outer envelope likewise containing a given quantity of neon. If this is not the case neon disappears through the wall of the discharge vessel with the result that the ignition voltage starts to increase again. This necessity of an outer envelope is not a drawback in itself because the discharge vessels referred to herein must be surrounded anyway by an outer envelope which must be evacuated or filled with nitrogen so as to reduce the heat radiation of the discharge vessel in order to obtain and maintain a sufficient vapour pressure of the iodides therein.

Lamps having an evacuated outer envelope usually contain a getter, for example, barium so as to maintain the vacuum. Lamps in which neon must be present in the outer envelope for the above-mentioned reason must also contain nitrogen in the outer envelope because otherwise flash-over between the current supply wires occurs easily. In these types of lamps a great drawback occurs. lt is true that the lamps ignite at a sufiiciently low voltage even after hundreds of operating hours, but they extinguish immediately after inition. Such a phenomenon has never been observed in otherwise identical lamps which did not have additions of other elements and iodine in the discharge vessel.

An analysis of this phenomenon carried out by means of many experiments made the inventors recognize that the extinction had to be a result of the presence of hydrogen in the outer envelope. This hydrogen originates from the discharge vessel and the iodides present therein and diffuses through the wall of the discharge vessel which generaly consists of quartz glass.

According to the invention a wall-stabilised highpressure mercury vapour discharge lamp having an ignition voltage of less than 500 volts consists of a quartz glass discharge vessel and an outer envelope encompassing this vessel, which discharge vessel contains in addition to mercury a mixture of neon and argon as well as iodide of at least one of the elements sodium, lithium, cadmium, thallium, indium, tin, dysprosium, scandium, gallium and lead and is characterized in that the space between the discharge vessel and the outerenvelope contains a mixture of nitrogen and neon and that a selective hydrogen getter is present in this space.

By providing a selective hydrogen getter in the outer envelope which is inactive for nitrogen and neon, but which binds hydrogen it was found that a substantially ideal lamp was produced which did not have any of the drawbacks of the known lamps. Although barium absorbs hydrogen satisfactorily, it cannot be used as agetto! because nitrogen is also present in the outer envelope. In such an atmosphere barium acts very poorly as a hydrogen getter.

The neon-argon mixture in the discharge vessel is preferably composed of from 0.1 to 5.0 percent by volume of argon and from 99.9 to 95.0 percent by volume of neon. The pressure of this mixture ranges from 10 to I00 torr at 20 C. The highest outputs are obtained at these values. The outer envelope contains preferably such a quantity of nitrogen that the pressure at 20C is between and 400 torr. The neon pressure in the outer envelope preferably ranges from 50 to 300 torr at 20 C. At these pressures the disappearance of neon into effect, it will now be described in detail, by way of example with reference to the accompanying diagrammatic drawing and a number of tests.

The drawing shows a lamp according to the invention intended for a load of 400 watts. The lamp has a quartz glass discharge vessel 1 the two ends of which have pinches 2 and 3 in which the seals 4 and 5 are provided. These seals are connected within the discharge vessel 1 to the electrodes 6 and 7. The current is applied to the electrodes 6 and 7 through the seals 4 and 5 and the wires 12 and 13. The wires 12 and 13 constitute a bracket in whichthe discharge vessel 1 is suspended by means of the pinches 2 and 3. The assembly of discharge vessel together with the bracket is present in an outer envelope 8 of hard glass one end of which has a pinch 9 through which the current supply wires 10 and 11 extend in a vacuum-tight manner. The bracket l2, 13 is provided with resilient strips 14 and 15 by which the bracket is resiliently supported within the outer envelope 8. A getter ring 16 containing zirconium metal is secured to the wire 13. The discharge vessel 1 has an internal diameter of 15.5 mms and a content of 7.5 cubic cms. The distance between the electrodes is 41 mms. The discharge vessel 1 contains a mixture of neon and 1 percent by volume of argon at a pressure of 40 torr. In addition to mercury the discharge vessel also includes the elements sodium, thallium and indium in the form of iodides. The outer envelope is filled with nitrogen up to a pressure of 200 torr and neon up to a pressure of 80 torr. r

The ignition voltage of a plurality of lamps according to the invention having a construction and a filling as described above with reference to the drawing was measured at different instants during their active lifetime. The measurements are summarized in column A of the Table below. For the purpose of comparison the same measurements were performed on two series of lamps B and C which are not according to the invention. The lamps B are completely analogous to the lamps according to the invention (A) with the difference that the zirconium gettering in the outer envelope is absent. The lamps C have a discharge vessel filled with argon up to a pressure of 20 torr and an evacuated outer envelope. Furthermore a barium getter is present in the outer envelopes of the lamps C. The construction and filling of the lamps C is otherwise equal to that of the lamps A.

It is clearly evident from the Table that the replacement of argon in the discharge vessel by a mixture of neon and argon only exerts little influence on the initial ignition voltage (compare the columns A and B with C). The increase of the ignition voltage during the lifetime is, however, largely prevented by this step. It was found from the measurements of the lamps B (without a hydrogen getter) that, although the ignition voltage remained sufficiently low during the lifetime, these lamps immediately extinguish after their ignition.

Operating Ignition voltage in Volts hours A B C lamps extinguish immediately after ignition.

To decrease the ignition voltage a bimetal strip may be secured to one of the current supply wires in the outer envelope of lamps according to the invention, which metal strip serves as an external ignition electrode and which in the cold condition engages the end of the discharge vessel near the electrode which is not connected to the said current supply wire. When heating the discharge vessel, the metal strip moves in such a manner that the contact with the wall of the discharge vessel is interrupted. This is necessary because it was found that the added elements present in the discharge vessel could disappear by electrolytical process through the quartz glass wall if in the hot condition a metal strip continued to engage the wall. In fact, this metal strip, relative to the nearest electrode, has a voltage which is equal to the operating voltage of the lamp.

It was found that lamps according to the invention for a load of 400 W and provided with the above-described ignition electrode could be ignited at the mains voltage of 220 V without using an ignition apparatus.

What is claimed is:

l. A wall-stabilised high-pressure mercury vapour discharge lamp having an ignition voltage of less than 500 volts and consisting of a quartz glass discharge vessel and a sealed outer envelope encompassing said vessel, which vessel contains in addition to mercury a mixture of neon and argon as well as iodide of at least one of the elements sodium, lithium, cadmium, thallium, indium, tin, dysprosium, gallium, lead and scandium, wherein the space between the discharge vessel and the outer envelope contains a mixture of nitrogen and neon and that a selective hydrogen getter is present in said space.

2. A high-pressure mercury vapour discharge lamp as claimed in claim 1, wherein the rare gas mixture in the discharge vessel consists of from 0.1 to 5.0 percent by volume of argon, and from 99.9 to 95.0 percent by volume of neon at a pressure of from 10 to torr at 20 C.

3. A high-pressure mercury vapour discharge lamp as claimed in claim 1 wherein the gas mixture between the discharge vessel and the outer envelope consists of nitrogen and neon, for which the pressure of neon at 20 C ranges from 50 to 300 torr and the pressure of nitrogen ranges trom 100 to 400 torr.

4. A high-pressure mercury vapour discharge lamp as claimed in claim 1 wherein the hydrogen getter comprises zirconium metal.

fl l t l 

2. A high-pressure mercury vapour discharge lamp as claimed in claim 1, wherein the rare gas mixture in the discharge vessel consists of from 0.1 to 5.0 percent by volume of argon, and from 99.9 to 95.0 percent by volume of neon at a pressure of from 10 to 100 torr at 20* C.
 3. A high-pressure mercury vapour discharge lamp as claimed in claim 1 wherein the gas mixture between the discharge vessel and the outer envelope consists of nitrogen and neon, for which the pressure of neon at 20* C ranges from 50 to 300 torr and the pressure of nitrogen ranges from 100 to 400 torr.
 4. A high-pressure mercury vapour discharge lamp as claimed in claim 1 wherein the hydrogen getter comprises zirconium metal. 